We wanted to find out whether students come across academic social media content serendipitously and, if so, to gain a detailed understanding of their experiences. To achieve this aim, we conducted semi-structured Critical Incident interviews with 15 postgraduate students from various disciplines. We found that the students did indeed come across academic social media content serendipitously – often when undertaking unfocused browsing during a break from other academic work. Time investment was identified as an important over-arching theme: investing time in creating and sharing social media content led to the creation of opportunities for serendipity for both the person creating/sharing the content and others. The interviews also highlighted a time investment trade-off – where more time spent using social media was perceived to provide greater opportunity for serendipity but, as serendipity can never be guaranteed, it was also perceived to increase the chance that none of the information encountered would contribute to the interviewees' academic research (and therefore would be ‘wasted’ time). We make a number of suggestions for the design of social media tools that create opportunities for serendipity based on our findings.